The rush to fix the VA mess is running into an age-old Washington problem: where to find the money.

Legislation to allow veterans facing long waits at Department of Veterans Affairs facilities to seek private healthcare could cost $50 billion or more a year, complicating efforts in Congress to swiftly come to agreement on a compromise bill.

The House and Senate have broken through the usual partisan gridlock on Capitol Hill and approved their own versions of legislation in response to problems faced by veterans in receiving healthcare in a timely manner. The legislation also follows revelations that VA staff falsified records to cover up the long waits.

But what so far has been a bipartisan response to the VA scandal showed strains Wednesday when the Republican-controlled House rejected, largely along party lines, a Democratic-led effort to instruct the chamber’s negotiators to accept the bill passed by the Senate last week.

Rep. Jeff Miller (R-Fla.), chairman of the House Veterans Affairs Committee, told Democrats, "I hope that I don’t see this vote used in any political ads."

House and Senate negotiators are due to begin working to reconcile their differences on VA reform, but the legislation is drawing scrutiny from budget watchdogs.

The Committee for a Responsible Federal Budget, a bipartisan nonprofit group, has warned that the Senate bill provides a "blank check to the VA, violates every principle of good budgeting, and could add substantially to the national debt."

The Congressional Budget Office has estimated that the House bill, when fully implemented, would cost the federal government about $54 billion a year, while the Senate measure would ultimately cost $50 billion a year.

Both measures would allow veterans living at least 40 miles from a VA facility or those unable to receive an appointment at a VA facility within the department’s wait-time goals from a VA facility to seek private care.

The Concord Coalition, in its blog, said Congress’ response to the VA healthcare scandal is to "throw money at the problem while throwing some veterans into a more costly and less effective system than the one they have been trying to access."

During debate on the VA bill last week, Sen. Jeff Sessions of Alabama, the top Republican on the Senate Budget Committee and one of three senators who voted against the bill, complained that the measure "sets no limits" on the healthcare spending but rather authorizes the VA to spend "such sums as necessary."

Sen. Rob Portman (R-Ohio), a former White House budget director who voted for the bill, said in a National Press Club speech Tuesday that it was important for Congress to come up with a "fiscally responsible" bill.

The issue promises to revive a debate over whether Congress should require spending cuts to other federal programs to offset increased spending for VA healthcare.

Sen. Bernie Sanders (I-Vt.), chairman of the Senate Veterans Affairs Committee, went to the Senate floor Tuesday to declare, "The cost of war is very expensive."

The House and Senate bills include a number of similarities, including expanding the VA secretary's authority to fire staff for poor performance.

But there still are a number of differences that must be reconciled.

The House bill would eliminate VA staff bonuses through 2016, which lawmakers said could save $400 million a year.

The Senate measure would authorize the department to lease 26 new health facilities in 17 states, including California, and Puerto Rico, and provide $500 million for expedited hiring of new VA doctors and nurses.